linux-kernel - [PATCH 5.4 017/261] sched/fair: Refill bandwidth before scaling

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Message-Id: <20200619141650.693573754@linuxfoundation.org>
Date:   Fri, 19 Jun 2020 16:30:28 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Huaixin Chang <changhuaixin@...ux.alibaba.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Ben Segall <bsegall@...gle.com>, Phil Auld <pauld@...hat.com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.4 017/261] sched/fair: Refill bandwidth before scaling

From: Huaixin Chang <changhuaixin@...ux.alibaba.com>

[ Upstream commit 5a6d6a6ccb5f48ca8cf7c6d64ff83fd9c7999390 ]

In order to prevent possible hardlockup of sched_cfs_period_timer()
loop, loop count is introduced to denote whether to scale quota and
period or not. However, scale is done between forwarding period timer
and refilling cfs bandwidth runtime, which means that period timer is
forwarded with old "period" while runtime is refilled with scaled
"quota".

Move do_sched_cfs_period_timer() before scaling to solve this.

Fixes: 2e8e19226398 ("sched/fair: Limit sched_cfs_period_timer() loop to avoid hard lockup")
Signed-off-by: Huaixin Chang <changhuaixin@...ux.alibaba.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Reviewed-by: Ben Segall <bsegall@...gle.com>
Reviewed-by: Phil Auld <pauld@...hat.com>
Link: https://lkml.kernel.org/r/20200420024421.22442-3-changhuaixin@linux.alibaba.com
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 kernel/sched/fair.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 8a0e6bdba50d..2f81e4ae844e 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4942,6 +4942,8 @@ static enum hrtimer_restart sched_cfs_period_timer(struct hrtimer *timer)
 		if (!overrun)
 			break;
 
+		idle = do_sched_cfs_period_timer(cfs_b, overrun, flags);
+
 		if (++count > 3) {
 			u64 new, old = ktime_to_ns(cfs_b->period);
 
@@ -4971,8 +4973,6 @@ static enum hrtimer_restart sched_cfs_period_timer(struct hrtimer *timer)
 			/* reset count so we don't come right back in here */
 			count = 0;
 		}
-
-		idle = do_sched_cfs_period_timer(cfs_b, overrun, flags);
 	}
 	if (idle)
 		cfs_b->period_active = 0;
-- 
2.25.1